A type of recording head that is called a side-shooter type head is available as an inkjet recording head (hereunder may be referred to as the “recording head”) that discharges ink onto a recording medium. The side-shooter type head discharges ink towards an upper side of a heater serving as an energy generating unit that generates energy used in discharging the ink. The basic structure of a recording head substrate of the side-shooter type head is shown in FIGS. 2A and 2B. In the recording head substrate shown in FIGS. 2A and 2B, an ink supply port 13 is provided in a silicon substrate 12 having heaters 11 formed at its surface. The ink supply port 13 is a through hole extending through the silicon substrate 12. Ink is supplied from a back-surface side of the silicon substrate 12 to a front-surface side of the silicon substrate 12 through the ink supply port 13.
A method of manufacturing the recording head substrate having the above-described structure is disclosed in U.S. Pat. No. 6,143,190. U.S. Pat. No. 6,143,190 discloses the manufacturing method including the following steps for preventing variations in an opening diameter of the ink supply port serving as a through hole.
The steps are:
(a) forming a sacrifice layer, which can be selectively etched with respect to a substrate material, at an ink supply port formation portion at the surface of the silicon substrate,
(b) forming an etching-resistant passivation layer at the silicon substrate so as to cover the sacrifice layer,
(c) forming an etching mask layer, having an opening provided in correspondence with the sacrifice layer, at the back surface of the silicon substrate,
(d) etching the silicon substrate by crystal-axis anisotropic etching until the sacrifice layer is exposed from the opening of the etching mask layer,
(e) etching the sacrifice layer from a portion where it is exposed by the etching step of the silicon substrate so as to remove it, and
(f) forming an ink supply port by removing a portion of the passivation layer.
The silicon-crystal-axis anisotropic etching used in the aforementioned step (d) is known as a technology that makes it possible to precisely form the ink supply port.
U.S. Pat. No. 6,805,432 discloses a manufacturing method in which, after performing dry etching using an etching mask layer provided at aback surface of a silicon substrate, crystal-axis anisotropic etching is performed using the same etching mask. According to this manufacturing method, a processing section that is L-shaped is formed. In this manufacturing method, the etching mask layer is used in common in both the dry etching and the wet etching. Therefore, an opening width (mask width) of the etching mask layer formed at the back surface of the silicon substrate and an excavation amount of dry etching determine an opening width of the ink supply port formed in the back surface of the silicon substrate. Here, the term “opening width” of the ink supply port refers to a short-side direction width of the ink supply port. The term “opening length” of the ink supply port refers to a long-side direction width of the ink supply port.
For achieving high-speed recording of a high-definition image, discharge openings are disposed very close together, and a larger number of discharge openings are disposed by making discharge opening rows longer. However, when the discharge opening rows are made longer, it is necessary to increase the opening length of the ink supply port. This may reduce mechanical strength of the substrate. The reduction in the mechanical strength causes deformation or breakage of the substrate in the process of manufacturing a recording head. It is known that, in particular, this causes an orifice plate to be peeled by the deformation of the substrate, and breakage when a chip is mounted.